1. Field of the Invention
The present invention relates to a liquid crystal display device and, in particular, to a shield member for cutting off electromagnetic wave and a technique suitable for grounding a drive control circuit.
2. Description of the Related Art
FIG. 4 is a schematic diagram showing a part of a conventional liquid crystal display device.
A liquid crystal display device 10 may use a cold-cathode tube 1 as the light source of the backlight. In the cases 4 and 9 of the liquid crystal display device 10, the light of the cold-cathode tube 1 is diffused by a light guide plate 5 or the like installed on the back side of a liquid crystal module 7, whereby it is possible to illuminate the entire surface of the liquid crystal module 7.
Connected to the both ends of the cold-cathode tube 1 are harnesses 2a and 2b for driving it. A connector 3 is attached to the forward end of the harnesses 2a and 2b so that a power source for applying voltage to the cold-cathode tube 1 may be connected. The harness 2a is formed so as to extend along the cold-cathode tube 1 and is accommodated in a groove 4a formed in the lower case 4 in parallel with the cold-cathode tube 1. The cold-cathode tube 1 driven by the harnesses 2a and 2b causes the light guide plate 5 to shine. The cold-cathode tube 1 and the harnesses 2a and 2b are covered with a cover 6, and above the lower case 4, there are provided the liquid crystal module 7 having printed circuit boards 8 on its sides and the upper case 9, and are secured to each other by screws. Drive circuits for driving the liquid crystal module 7 and the cold-cathode tube 1 are formed on these printed circuit boards 8, and drive LSIs for driving the common electrode and the segment electrode of the liquid module 7 are mounted thereon.
In such a conventional liquid crystal display device, a metal cover formed of tin or the like and surrounding the cold-cathode tube 1, the liquid crystal module 7, etc. may be provided on the inner side of the cases 4 and 9, the metal cover being connected to the cases 4 and 9 through the intermediation of a flange or the like provided on the outer side thereof.
The metal cover provided in the conventional liquid crystal display device is connected to the case through the intermediation of a flange or the like for the purpose of dissipating static electricity to the case. However, there is a demand for using this metal cover as an EMI (electromagnetic interference) member for cutting off the electromagnetic wave generated from the cold-cathode tube 1, the liquid crystal module 7, etc. to improve the operational stability of the printed circuit boards.
Further, there is a demand for utilizing this metal cover to ground the drive circuits, etc. by connecting it to the printed circuit boards 8, etc. For this purpose, it is necessary to make it possible to solder the printed circuit boards 8, etc.
Further, when utilizing the metal cover to ground the drive circuits, etc., it is necessary to press it against the inner surface of the case, etc. to reliably effect connection. For this purpose, elasticity is required, which cannot be expected of tin.
Furthermore, when utilizing the metal cover to ground the drive circuits, etc., it is necessary for the entire metal cover to exhibit equal potential even when there is a difference in impedance between different portions of the metal cover connected to the drive circuits, etc. to secure the operational stability of the drive circuits.
The present invention has been made in view of the above requirements. Accordingly, the present invention aims to achieve the following objects.
(1) To improve the property of cutting off the electromagnetic wave generated from the liquid crystal module and the backlight portion inside the shield member.
(2) To make it possible to ground the liquid crystal display device with respect to the drive control circuit.
(3) To improve the operational stability of the liquid crystal display device.
To achieve the above objects, there is provided, in accordance with the present invention, a liquid crystal display device comprising a shield member which is made of an elastic metal and which includes a casing portion having an opening and a plate portion substantially closing the opening, wherein the casing portion has in the entire periphery surrounding the opening a plurality of spring fingers protruding elastically outward and arranged in parallel with each other, and an outer case connected to the shield member through the intermediation of the spring fingers, wherein a liquid crystal module and a backlight portion for illuminating the screen of the liquid crystal module are arranged inside the shield member, and wherein a substrate of a drive control circuit for driving and controlling the liquid crystal module and the backlight portion is arranged outside the shield member.
In the present invention, when an electromagnetic wave is generated inside the shield member, it is possible to cut off the electromagnetic wave. and the static electricity of the shield member can be easily dissipated to the exterior by the plurality of spring fingers, so that it is possible to maintain the shield member at an equal potential.
Further, due to this arrangement, it is possible to cut off the electromagnetic waves emitted from the liquid crystal module, the backlight portion, etc., and it is possible to prevent malfunction of the electronic parts such as ICs and LSIs on the substrate. Further, it is possible to connect the shield member with the outer case by the spring fingers, and the static electricity of the shield member can be dissipated to the exterior. Further, it is possible to reduce the contact resistance between the spring fingers and the outer case.
In the present invention, it is possible for the plurality of spring fingers to be arranged substantially at equal intervals, the interval being preferably 20 mm or less and, more preferably, 15 mm or less.
In accordance with the present invention, the interval of the spring fingers is determined to be 20 mm or less and, more preferably, 15 mm or less, so that it is possible to make the entire potential of the shield member more uniform.
The spring fingers are arranged in parallel with each other, and in parallel with the thickness direction of the liquid crystal module, and the shield member can be integrally provided with a ground connection portion connected to the grounding portion of the substrate.
Due to this arrangement, the shield member can be smoothly fitted in the outer case when assembling the outer case and the shield member.
Further, since the metal shield member is integrally provided with the ground connection portion, it is possible to solder the ground connection portion to the substrate.